This invention is directed toward bicycle brakes, and more particularly toward a caliper drive for a ball bearing mechanical disc brake caliper.
Disc brakes are being included on more and more bicycles as consumers are ever increasingly demonstrating a preference for disc brakes over conventional rim brakes such as caliper brakes, cantilever brakes and side pull cantilever brakes. To date, consumers have demonstrated a preference for hydraulic disc brakes as opposed to ball bearing mechanical disc brakes because of a perception that hydraulic disc brakes are more powerful and provide smoother and easier actuation. However, hydraulic disc brakes are relatively expensive because of, in part, tight tolerances that must be maintained in the manufacturing of components to provide necessary fluid seals between moving parts. While ball bearing mechanical disc brakes have a cost advantage, interaction between the moving parts leads to friction which makes actuation relatively difficult. In addition, ball bearing mechanical disc brakes typically require assembly of a large number of parts which increases assembly complexity and attendant costs.
The present invention is directed toward overcoming one or more of the problems discussed above.
A caliper drive for a bicycle ball bearing mechanical disc brake caliper is configured for moving an associated brake pad along an advancement axis relative to a brake disc operatively associated with the ball bearing mechanical disc brake caliper during caliper actuation. The caliper drive includes a first or fixed cam which is fixed against axial movement relative to the advancement axis during caliper actuation and a second or drive cam movable axially of the advancement axis relative to the first cam during caliper actuation. A plurality of ramped grooves are between the first cam and the second cam, each ramped groove receiving a ball bearing. The ramped grooves are configured to cause axial movement of the second cam relative to the first cam upon relative rotation of the cams about the advancement axis. Each ramp has a sidewall defining a radially stable path for the ball bearing, with the sidewalls substantially preventing relative radial movement between the first and second cams. A cooperating ramped groove may be operatively associated with each ramped groove to form a cooperative ramped groove pair. The ball bearing is received between each cooperative ramped groove pair and the ramped groove and cooperative ramped groove of each cooperative ramped groove pair extends circumferentially in opposite directions relative to the advancement axis. Each ramped groove may extend circumferentially at an identical radius about the advancement axis.
Another aspect of the present invention is a caliper drive for a bicycle ball bearing mechanical disc brake caliper including a ramp configuration that increases the length of the grooves to facilitate greater rotational movement of the drive cam per unit of axial advancement of the drive cam during brake actuation. The caliper drive includes a first cam fixed against axial movement relative to an advancement axis during caliper actuation and a second cam movable axially of the advancement axis relative to the first cam during caliper actuation. A plurality of elongate ramped grooves reside between the first and second cams with each groove receiving a ball bearing and being configured to cause axial movement of the second cam relative to the first cam upon relative rotation of the cams about the advancement axis. Each groove extends circumferentially about the advancement axis and the grooves are circumferentially spaced relative to each other about the advancement axis. Each groove further has a radius from the advancement axis that varies uniformly with respect to the other ramped grooves. Adjacent ramped grooves overlap in a radial direction over a portion of the length.
The caliper drive of the present invention provides ramped grooves between a fixed cam and a drive cam which act like a angular contact bearing to accommodate radial loads on the drive cam resulting from actuation of the caliper drive. Because the walls of the grooves bear this radial load, a bushing or bearing which might otherwise need to be employed between the drive and fixed cams can be eliminated. This not only decreases part costs, it further minimizes assembly complexity, thereby providing a lower cost caliper drive. In addition, it minimizes friction between the drive and fixed cams. Providing radially overlapping grooves of varying radius allows for greater rotational movement of the drive cam relative to the fixed cam per unit of axial advancement of the fixed cam, thereby providing a mechanical advantage enabling a more xe2x80x9cpowerfulxe2x80x9d ball bearing mechanical disc brake.